Packaging a reconfigurable optical add-drop module
View Patent ↗A hermetically packaged, MEMS array-based ROADM module is disclosed. The enclosure sidewalls and a top lid are made of Kovar, and the base is made of alumina ceramic AuSn-soldered to the enclosure sidewalls. The MEMS array is attached to the ceramic base. The optics are passively pre-aligned using a removable template and epoxied to an optical bench. The optical bench is actively aligned as a whole and attached to the ceramic base. A plurality of electrical feedthrough contact pins extend from the bottom of the ceramic base for connecting the MEMS to a connector on a printed circuit board. In one embodiment of the invention, the ceramic base extends beyond the footprint of the sidewalls of the enclosure of the module, for mounting additional electronic components, for example MEMS driver circuitry chips, directly to the ceramic base of the enclosure.
1. A reconfigurable optical add-drop module comprising:
an input optical port for launching an input optical signal having a plurality of wavelength channels;
an output optical port for outputting an output optical signal having at least one of said wavelength channels;
a dispersive optical element optically coupled to the input optical port and to the output optical port, for spatially dispersing the input optical signal into individual wavelength channels, and for recombining the at least one wavelength channel into the output optical signal;
an optical switching engine optically coupled to the dispersive optical element, for spatially redirecting the at least one wavelength channel from the input optical port to the output optical port;
a plurality of optical components for providing optical coupling of the dispersive element to the input optical port, to the output optical port, and to the optical switching engine;
an optical bench for supporting the dispersive optical element and the plurality of optical components in a fixed relationship therebetween; and
an enclosure for packaging the optical switching engine and the optical bench having the optical elements mounted thereon, the enclosure having: a base for supporting the optical bench and the optical switching engine, a closed sidewall attached to the base, wherein the sidewall surrounds the optical bench and the optical switching engine, and a lid attached to the sidewall, for sealing the enclosure;
wherein at least a portion of the base comprises a ceramic board for supporting the optical switching engine,
wherein at least a portion of said ceramic board is mechanically accessible from both inside and outside of the enclosure,
wherein said accessible portion of ceramic board has electrical feedthroughs coupled to said optical switching engine, and
wherein said feedthroughs are mechanically and electrically accessible from the outside of the enclosure.
2. A reconfigurable optical add-drop module of claim 1 , wherein the enclosure is a hermetically sealed enclosure.
3. A reconfigurable optical add-drop module of claim 2 , wherein the optical switching engine comprises a MEMS array.
4. A reconfigurable optical add-drop module of claim 3 , wherein the MEMS array is wirebonded to contact pads disposed on the ceramic board, wherein said contact pads are electrically coupled to the electrical feedthroughs in the ceramic board.
5. A reconfigurable optical add-drop module of claim 1 , wherein the dispersive element comprises a diffraction grating.
6. A reconfigurable optical add-drop module of claim 1 , wherein the ceramic board is smaller than the base.
7. A reconfigurable optical add-drop module of claim 1 , wherein the ceramic board is the base.
8. A reconfigurable optical add-drop module of claim 7 , wherein the ceramic board has a footprint, and wherein the sidewall has a footprint in a plane of the ceramic board's footprint, and wherein the footprint of the ceramic board is larger than the footprint of the sidewall, the reconfigurable optical add-drop module further comprising electronic components attached to the ceramic board outside of the footprint of the sidewall.
9. A reconfigurable optical add-drop module of claim 1 , wherein the sidewall is made of Kovar.
10. A reconfigurable optical add-drop module of claim 1 , wherein the optical bench is attached to the base with at least two posts having a polygonal cross-section.
11. A reconfigurable optical add-drop module of claim 1 , wherein the ceramic board has a footprint at least 50 mm wide and at least 70 mm long.
12. A method of assembly of the reconfigurable optical add-drop module of claim 1 , comprising:
(a) aligning the optical elements and the dispersive optical element to the optical bench;
(b) upon completion of step (a), fixing said optical and dispersive optical elements to the optical bench;
(c) attaching the base to the sidewall;
(d) attaching the optical switching engine to the ceramic board, and electrically coupling said optical switching engine to the feedthroughs in the ceramic board;
(e) upon completion of steps (b) and (d), aligning the optical bench to the optical switching engine, so as to provide the optical coupling between the optical switching engine on the ceramic board and the dispersive element on the optical bench;
(f) upon completion of step (e), attaching the optical bench to the base; and
(g) upon completion of step (f), attaching the lid to the sidewall, so as to seal the enclosure.
13. A method of assembly of claim 12 , wherein in step (a), said aligning is performed by affixing a template to the optical bench, and by placing the optical elements and the dispersive optical element into the template.
14. A method of assembly of claim 13 , wherein in step (b), said fixing is performed by epoxying the optical elements and the dispersive optical element to the optical bench.
15. A method of assembly of claim 12 , wherein in step (c), said attaching is performed by soldering.
16. A method of assembly of claim 15 , wherein said soldering is performed by using an AuSn alloy having melting temperature of 280+−40 C.
17. A method of assembly of claim 12 , wherein in step (d), said electrical coupling is performed by wirebonding.
18. A method of assembly of claim 12 , wherein in step (e), said aligning includes:
(h) bringing the optical bench to the optical switching engine;
(i) launching a test input optical signal into the input optical port, wherein the test input optical signal has a pre-determined optical power level;
(j) detecting a test output optical signal at the output optical port; and
(k) adjusting the position of the optical bench relative to the optical switching engine, so as to achieve a pre-defined optical power level of the test output optical signal.
19. A method of assembly of claim 12 , wherein in step (f), said attaching is performed by using at least two posts having a polygonal cross-section, wherein each of said posts are attached to both the optical bench and the base.
20. A method of assembly of claim 12 , wherein in step (g), said attaching is performed by welding or soldering.